Figure 1.
Schematics of target configuration during head-alone (H-alone) tracking, head-gaze (H–G) pursuit and eye-head combined (E–H) gaze shifts.
GS: gaze target re space (blue). JS: juice spout position re space (red). JH: juice spout position re head (green). G′S, J′S, and J′H represent the initial positions for gaze target re space, juice spout re space, and juice spout re head, respectively. Note during head-alone tracking and head-gaze pursuit, the juice spout was rotated in the same angular velocity as the gaze target motion, whereas during eye-head combined gaze shifts, the juice spout was attached to and rotated with the head.
Figure 2.
Two examples of submovement composition during head-alone tracking.
Top two rows depict position (top) and velocity (middle) traces, respectively, separated for gaze movement (G; blue), head movement (H; red), eye movement (E, re head; gray), and juice spout motion (Js; green). Bottom panels depict the profiles of the head velocity (H, thin red) and the minimum-jerk model of head velocity (Hmj, thick gray). Task-associated head movement was selected between the onset (▴) and offset (▾) of juice spout motion. The order of the submovements is coded in color (first: magenta; second: green; third: light blue). Time scale is identical across all plots. To facilitate data comparison, the head movements are plotted in positive directions regardless of whether the movements were rightward or leftward, the other movements were rectified accordingly. Note the goodness of fit in B improved by 55.1% from a single submovement model (#SM = 1; 55.5% error) to two overlapping submovement model (#SM = 2; 0.4% error).
Figure 3.
Two examples of submovement composition of head movement during head-gaze pursuit.
Note the goodness of fit in A improved by 83.8% from one single submovement (#SM = 1; 84.9% error) to 2 overlapping submovements (#SM = 2; 1.1% error). The goodness of fit in B improved by 8.1% from a single submovement (#SM = 1; 8.3% error) to 2 overlapping submovements (#SM = 2; 0.2% error). Format after Figure 2.
Figure 4.
Three examples of submovement composition of head movement during eye-head combined gaze shifts.
For stationary gaze target (A–B), task-associated head movement, indicated as arrowheads ▴ and ▾, was included up to the end of gaze target display (A) or the onset of correction saccade when correction gaze shifts occurred (B). For flashed gaze target (C), task-associated head movement was included up to 200 ms following gaze end. Note the goodness of fit in A improved by 18.9% from a single submovement (#SM = 1; 19.1% error) to 3 overlapping submovements (#SM = 3; 0.2% error). The goodness of fit in B improved by 6.1% from a single submovement (#SM = 1; 6.3% error) to 2 overlapping submovements (#SM = 2; 0.2% error). Same format as in Fig. 2.
Figure 5.
Two examples of the DOI and PDI measures and PDI vs. DOI scattergrams during head tracking movement and eye-head combined gaze shifts.
The regression line across the data in B is a least-square function. The movement plotted in Fig. 3A is shown in the inset of B. Od: duration of submovement overlap; Fd: duration of the first submovement; Sd: duration of the second submovement; Iv: intercepted velocity between the first and second submovements: Sv: peak velocity of the second submovement. Data includes only overlapping submovements.
Figure 6.
Head tracking movements and eye-head combined gaze shifts distinguished by the peak velocity ratio between the second and the first submovements as a function of submovement amplitude.
The regression lines are least-square functions. The horizontal dashed lines indicate when the second submovements had the same values in peak velocity as the first submovement. Data includes only overlapping submovements.
Figure 7.
Head tracking movements and eye-head combined gaze shifts distinguished by peak velocity as a function of submovement amplitude.
Data includes all submovements.
Figure 8.
Head tracking movements and eye-head combined gaze shifts distinguished by submovement duration as a function of peak velocity.
A: Data separated for head tracking and eye-head combined gaze shifts. B: Same data as in A, separated for first and second submovements. Data is plotted as mean ± S.D. Note during head tracking, the submovements exhibited relatively longer duration independent of peak velocity. This tendency persisted for the first and second submovements.
Figure 9.
Head tracking movements and eye-head combined gaze shifts distinguished by normalized peak velocity (peak velocity×duration−1) as a function of submovement amplitude.
Peak velocity and duration are computed after the example shown in Figure 6. Data is plotted as mean ± S.D. Note the submovements exhibited relatively higher normalized peak velocity during eye-head combined gaze shifts compared to head tracking movement. This tendency persisted independent of movement amplitude and the order of the submovements.